Paper container for liquid

Abstract

Disclosed is a paper container for liquid, the paper container sequentially including, in the following order, a paper base material layer, an easily releasable layer, and a sealant layer that is adjacent to the easily releasable layer. The easily releasable layer includes a high pressure, low density, polyethylene (A) and a propylene resin (B). The content of the high pressure, low density, polyethylene (A) in the easily releasable layer is 50 mass% or more relative to the total content of the high pressure, low density, polyethylene (A) and the propylene resin (B). The sealant layer contains a polyethylene resin (C).

Description

Liquid cartons

[0001] The present disclosure relates to a liquid carton.

[0002] Resin or glass containers are commonly used as containers for liquid foods such as dairy products, fruit juice drinks, alcoholic beverages, and edible oils from the viewpoint of shelf life. In recent years, for example, paper containers using a paper base material have been attracting attention in order to reduce the amount of resin used. Paper containers are containers using a paper base material whose surface is coated with a resin such as polyethylene, and are formed by closely adhering laminates having the paper base material. From the viewpoint of shelf life of the contents, paper containers are required to have high adhesion, and the containers are also required to be easy to open when used. Furthermore, since the paper base material of paper containers is recyclable, the ease of disassembling the container after use is also important from the viewpoint of ease of recycling.

[0003] For example, Patent Document 1 (JP 2013-119433 A) discloses a paper container for liquids with a gable roof-shaped top, which is made by folding and molding the laminate, which uses a paperboard base layer and has a surface layer with heat fusion properties, a base layer, an intermediate layer with gas barrier properties, and a sealant layer laminated in that order, the sealant layer containing a specific amount of thermoplastic elastomer, with the sealant layer facing the inner surface.

[0004] Patent Document 1: Japanese Patent Application Laid-Open No. 2013-119433

[0005] The performance requirements for paper containers for liquids are becoming increasingly stringent. Generally, paper containers are formed into various shapes by folding a laminate based on a paper substrate and tightly adhering the laminated bodies together. Specific performance requirements include high peel strength to prevent leakage of contents due to opening of the sealed joints caused by vibrations during transportation or stresses during stacked storage, easy peelability to allow easy opening at the time of use, and easy disassembly for recycling after use. Particularly in the case of dairy products, edible oils, and the like, undesired opening of the sealed joints not only leads to a deterioration in quality but also significantly impairs the appearance of the paper container.

[0006] The problem that one embodiment of the present disclosure aims to solve is to provide a paper container for liquid that maintains peel strength within an appropriate range, has good liquid preservation properties, and is easy to open and disassemble.

[0007] Specific means for solving the above problems include the following aspects: <1> A paper container for liquids, comprising a paper base layer, an easily peelable layer, and a sealant layer adjacent to the easily peelable layer, in this order, wherein the easily peelable layer contains a high-pressure low-density polyethylene (A) and a propylene-based resin (B), the content of the high-pressure low-density polyethylene (A) in the easily peelable layer is 50 mass% or more relative to the total content of the high-pressure low-density polyethylene (A) and the propylene-based resin (B), and the sealant layer contains a polyethylene-based resin (C).

[0008] <2> The paper container for liquids according to <1>, further comprising a barrier layer between the paper base layer and the easily peelable layer. <3> The paper container for liquids according to <2>, further comprising an aluminum foil, an aluminum vapor-deposited film, and a transparent vapor-deposited film.

[0009] <4> The paper container for liquids according to any one of <1> to <3>, wherein the polyethylene resin (C) in the sealant layer comprises at least one selected from high-pressure low-density polyethylene and linear low-density polyethylene. <5> The paper container for liquids according to any one of <1> to <4>, wherein the high-pressure low-density polyethylene (A) in the easily peelable layer has a melting point in the range of 100°C to 125°C.

[0010] <6> The paper container for liquids according to any one of <1> to <5>, wherein the propylene-based resin (B) in the easily peelable layer includes a propylene homopolymer (B1). <7> The paper container for liquids according to any one of <1> to <6>, wherein the total content of the high-pressure low-density polyethylene (A) and the propylene-based resin (B) in the easily peelable layer is 50% by mass or more and 100% by mass or less, based on the total mass of the solids contained in the easily peelable layer. <8> The paper container for liquids according to any one of <1> to <7>, wherein the content of the thermoplastic elastomer in the easily peelable layer is less than 10% by mass, based on the total mass of the solids contained in the easily peelable layer.

[0011] <9> The paper container for liquids according to any one of <1> to <8>, wherein the content of the polyethylene resin (C) in the sealant layer is more than 95% by mass based on the total mass of the solid content contained in the sealant layer.

[0012] <10> The paper container for liquids according to any one of <1> to <9>, wherein the easily peelable layer further contains a tackifier resin (D). <11> The paper container for liquids according to <10>, wherein the total content of the high-pressure low-density polyethylene (A), the propylene-based resin (B), and the tackifier resin (D) in the easily peelable layer exceeds 90% by mass based on the total mass of solids contained in the easily peelable layer.

[0013] <12> The paper container for liquid according to any one of <1> to <11>, which is a brick-type box-shaped paper container or a gable-top box-shaped paper container.

[0014] According to one embodiment of the present disclosure, a paper container for liquid is provided that maintains peel strength within an appropriate range, has good liquid preservation properties, and is easy to open and disassemble.

[0015] Fig. 1 is a schematic structural diagram showing an example of a laminate that forms a paper container for liquid of the present disclosure. Fig. 2 is a perspective view showing an example of a brick-type box paper container that is a paper container for liquid of the present disclosure. Fig. 3A is a perspective view showing an example of a gable-top box paper container that is a paper container for liquid of the present disclosure. Fig. 3B is a perspective view showing an example of a gable-top box paper container that has a spout on the gable roof portion of the gable top.

[0016] Hereinafter, embodiments of the present disclosure will be described in detail, but the present disclosure is not limited to the following embodiments.

[0017] In this disclosure, numerical ranges indicated using "to" indicate ranges that include the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another staged numerical range. Furthermore, in numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples. In this disclosure, each component may contain multiple corresponding substances. When multiple substances corresponding to each component exist, the content or amount of each component refers to the total content or amount of the multiple substances, unless otherwise specified. In this disclosure, "layer" and "film" include not only configurations of shapes formed over the entire surface when observed in a plan view, but also configurations of shapes formed only on a portion. Components indicated with the same reference numeral in each drawing in this disclosure are the same components. Dimensional ratios in the drawings do not necessarily represent actual dimensional ratios.

[0018] In the present disclosure, high-pressure low-density polyethylene (hereinafter sometimes referred to as HP-LDPE) is a polyethylene having a density of 910 kg / m3 synthesized by radical polymerization under a high pressure of 100 MPa to 400 MPa. ３ More than 930kg / m ３ HP-LDPE refers to polyethylene with a density of less than 1000 MPa. HP-LDPE is synthesized by a high-pressure method and has a structure in which repeating ethylene units are randomly branched. For this reason, it has the characteristics of a lower melting point and greater flexibility than linear low-density polyethylene (hereinafter sometimes referred to as L-LDPE), which is a copolymer generally obtained by copolymerizing ethylene with an α-olefin such as 1-butene using a metallocene catalyst.

[0019] [Paper container for liquids] The paper container for liquids of the present disclosure comprises, in this order, a paper base material, an easily peelable layer, and a sealant layer adjacent to the easily peelable layer, wherein the easily peelable layer contains a high-pressure low-density polyethylene (A) and a propylene-based resin (B), the content of the high-pressure low-density polyethylene (A) in the easily peelable layer is 50 mass% or more relative to the total content of the high-pressure low-density polyethylene (A) and the propylene-based resin (B), and the sealant layer contains a polyethylene-based resin (C). The paper container for liquids of the present disclosure is suitable for storing liquids, particularly liquid foods such as edible oils and dairy products, has good storage stability, reduces undesired container breakage during storage and transportation, is easy to open when in use, and can be easily disassembled for recycling after use.

[0020] The paper container for liquids of the present disclosure has an easily peelable layer containing high-pressure low-density polyethylene (i.e., HP-LDPE) (A) and a propylene-based resin (B), and the content of HP-LDPE (A) relative to the total content of HP-LDPE (A) and propylene-based resin (hereinafter sometimes referred to as PP) (B) is 50% by mass or more, so that a sea-island structure of two resins, HP-LDPE (A) and PP (B), is formed in the easily peelable layer. Because the content of HP-LDPE (A) in the easily peelable layer is relatively high compared to the propylene-based resin (B), the easily peelable layer as a whole maintains stable peel strength, and upon opening, an appropriately low peel strength is achieved at the interface with the sealant layer containing polyethylene-based resin (C), which is thought to facilitate easy opening and easy peeling between layers. That is, since the sealant layer adjacent to the easily peelable layer contains the polyethylene resin (C), it has good affinity with the HP-LDPE (A) in the easily peelable layer, and it is thought that when the package is left to stand, the adhesion between the easily peelable layer and the sealant layer is good, and when stress is applied when the package is opened, the peelability between the layers is good.

[0021] <Easily Peelable Layer> The easily peelable layer in the paper container for liquids of the present disclosure (hereinafter also simply referred to as the easily peelable layer) contains high-pressure low-density polyethylene (A) (HP-LDPE(A)) and a propylene-based resin (B) (PP(B)), and the content of HP-LDPE (A) is 50% by mass or more relative to the total content of HP-LDPE (A) and PP (B). The easily peelable layer can be formed by forming a film of a resin composition for forming an easily peelable layer, which contains HP-LDPE (A) and PP (B) in the above-mentioned amounts and further contains other components that are used in combination as desired. Each component contained in the easily peelable layer will be described below.

[0022] —High-Pressure Low-Density Polyethylene (A) (ie, HP-LDPE (A))— The HP-LDPE (A) used in the easily peelable layer of the present disclosure is polyethylene obtained by polymerizing ethylene by a high-pressure radical method.

[0023] The polymerization of HP-LDPE can be carried out by a known method. The reactor used for the polymerization includes, for example, an autoclave reactor and a tubular reactor, and either may be used.

[0024] The HP-LDPE (A) that can be contained in the easily peelable layer in the present disclosure has a density of 910 kg / m as measured in accordance with JIS K7112:1999 "Measurement of density and specific gravity of non-foamed plastics." ３ More than 930kg / m ３ and preferably 915 kg / m ３ More than 925kg / m ３ The density is in the following range: By using HP-LDPE (A) having a density in the above range for the resin composition for forming the easily peelable layer, a resin composition having excellent extrusion processability can be obtained.

[0025] Furthermore, the HP-LDPE (A) contained in the easily peelable layer preferably has a melt flow rate (hereinafter sometimes referred to as MFR) measured in accordance with JIS K 7210-1:2014 under conditions of 190°C and a load of 2160 g of 1.0 g / 10 min or more and 100 g / 10 min or less, more preferably 1.0 g / 10 min or more and 80 g / 10 min or less, and even more preferably 3.0 g / 10 min or more and 70 g / 10 min or less. By using HP-LDPE (A) having a melt flow rate within the above range in the resin composition for forming the easily peelable layer, the extrusion processability when forming the easily peelable layer becomes better.

[0026] The HP-LDPE (A) contained in the easily peelable layer preferably has a melting point, measured by a differential scanning calorimeter (DSC) in accordance with JIS K7121:1987, of 100° C. to 120° C., more preferably 103° C. to 115° C. By using HP-LDPE (A) having a melting point within the above range in the resin composition for forming the easily peelable layer, a resin composition that is excellent in extrusion processability and good in easy peelability can be obtained.

[0027] The content of HP-LDPE (A) in the easily peelable layer is 50% by mass or more, preferably 55% by mass or more, and more preferably 60% by mass or more, based on the total content of HP-LDPE (A) and the propylene-based resin (i.e., PP (B)) described below in the easily peelable layer. There is no particular upper limit on the content of HP-LDPE (A) based on the total content of HP-LDPE (A) and PP (B), but it can be 99% by mass or less, and preferably 80% by mass or less. When the content of HP-LDPE (A) in the easily peelable layer is within the above range, it becomes easy to control the heat resistance and peel strength of the easily peelable layer within appropriate ranges.

[0028] - Propylene-based resin (PP(B)) - The easily peelable layer contains a propylene-based resin (B) (i.e., PP(B)). PP(B) may be one selected from the group consisting of propylene-based resins, i.e., copolymers and homopolymers having structural units derived from propylene. PP(B) may contain only one type, or may contain two or more types having different molecular weights. PP(B) may be a propylene homopolymer (B1). From the viewpoint of formability and impact resistance of the easily peelable layer, it is preferable that PP(B1), which is a preferred embodiment of PP(B), has a crystallinity of 30% or more by X-ray.

[0029] From the viewpoint of heat resistance, PP (B) is preferably a polymer having a melting point of 120°C to 170°C, more preferably 150°C to 170°C, as measured by a differential scanning calorimeter (DSC) in accordance with JIS K7121:1987.

[0030] PP (B1), which is a preferred embodiment of the above-mentioned PP (B), can be produced by polymerizing propylene in the presence of a stereoregular olefin polymerization catalyst containing a titanium-based or metallocene-based transition metal compound component, an organoaluminum component, and, if necessary, an electron donor, a carrier, etc.

[0031] The melt flow rate (MFR) of PP(B) measured under a load of 2.16 kg and at a temperature of 230°C is preferably 1 g / 10 min to 500 g / 10 min, more preferably 2 g / 10 min to 100 g / 10 min, and even more preferably 3 g / 10 min to 50 g / 10 min, from the viewpoints of moldability and impact resistance. The MFR of PP(B) is a value measured in accordance with JIS K 7210-1:2014 under conditions of a test load of 2.16 kg and a temperature of 230°C.

[0032] The density of PP (B) is 870 kg / m from the viewpoint of excellent impact resistance and a low linear expansion coefficient. ３ ~930 kg / m ３ is preferred, and 880 kg / m ３ ~920 kg / m ３ More preferably, 890 kg / m ３ ~910 kg / m３ The density of PP(B) is a value measured by the underwater displacement method in accordance with JIS K 7112:1999.

[0033] The content of PP (B) in the easily peelable layer is preferably more than 0 mass% and less than 40 mass%, more preferably 20 mass% or more and 39 mass% or less, and even more preferably 25 mass% or more and 38 mass% or less, relative to the total mass of the easily peelable layer.

[0034] It is believed that the easily peelable layer contains PP (B), which has poor compatibility with the aforementioned HP-LDPE (A), thereby achieving a good balance between peel strength and ease of releasability in the easily peelable layer. When opening or dismantling a container, there are three types of peeling mechanisms that occur when peeling the sealed portions of the container: interfacial peeling, interlayer peeling, and cohesive peeling. In the paper container for liquids according to the present disclosure, a laminate of a paper base material, an easily peelable layer, and a sealant layer adjacent to the easily peelable layer is assembled into a container shape and then heat-sealed. When opening the paper container, peeling is believed to occur by interlayer peeling between the easily peelable layer containing HP-LDPE (A) and the sealant layer containing a polyethylene resin (C).

[0035] Although the function of the present disclosure is not clear, as described above, a resin composition for forming a peelable layer is formed by mixing HP-LDPE (A) and PP (B), which has poor compatibility with HP-LDPE (A). When forming the peelable layer, a sea-island structure is formed in which HP-LDPE (A) forms the sea and PP (B) forms the islands. High adhesion strength is achieved in the overlapping portion of the paper base layer and the sealant layer containing polyethylene-based resin (C) due to the adhesive function of HP-LDPE (A) forming the sea structure. When peeling the overlapping portion, it is believed that interlayer delamination occurs at the interface between the peelable layer and the sealant layer containing polyethylene-based resin (C), resulting in good peelability.

[0036] The content of HP-LDPE (A) is preferably 50% by mass or more relative to the total content of HP-LDPE (A) and PP (B) in the easily peelable layer. The content ratio of HP-LDPE (A) to PP (B) in the easily peelable layer ((A):(B)=) is preferably 80:20 to 50:50 in mass terms, and more preferably 75:25 to 55:45 in mass terms.

[0037] -Other Components- In addition to HP-LDPE (A) and PP (B), the easily peelable layer according to the present disclosure may contain components other than those described above (also referred to as "other components") depending on the purpose, as long as the effects are not impaired. The other components are not particularly limited, but examples thereof include thermoplastic elastomers, tackifier resins, antistatic agents, antiblocking agents, slip agents, antioxidants, heat stabilizers, light stabilizers, pigments, dyes, etc. The other components may be used alone or in combination of two or more. Other components may be included depending on the purpose.

[0038] Even when other components are contained, it is preferable from the viewpoint of effectiveness that the total content of the HP-LDPE (A) and the PP (B) in the easily peelable layer according to the present disclosure is 50% by mass or more and 100% by mass or less, based on the total mass of the solid content contained in the easily peelable layer.

[0039] Thermoplastic Elastomer The peelable layer may further contain a thermoplastic elastomer, and the content of the thermoplastic elastomer in the peelable layer is preferably less than 10% by mass relative to the total mass of the solids contained in the peelable layer. Examples of thermoplastic elastomers that the peelable layer may contain include polyolefin-based thermoplastic elastomers such as modified ethylene-α-olefin copolymers, polybutene-1, polymethyl-1-pentene, polyhexene-1, and polyoctene-1; polystyrene-based thermoplastic elastomers such as styrene-isoprene copolymers and hydrogenated styrene-isoprene copolymers; polyester-based thermoplastic elastomers; polyurethane-based thermoplastic elastomers; polyamide-based thermoplastic elastomers; chlorinated polymer-based thermoplastic elastomers; and fluorine-based thermoplastic elastomers. When the peelable layer contains a thermoplastic elastomer, the content of the thermoplastic elastomer is preferably less than 10% by mass relative to the total mass of the solids contained in the peelable layer, and is preferably 5% by mass or less. It may also be greater than 0% by mass and up to 5% by mass, or the peelable layer may not contain a thermoplastic elastomer.

[0040] - Tackifier resin (D) - The peelable layer may further contain a tackifier resin (D). The tackifier resin (D) has the function of imparting tackiness to the resin. This makes it easy to adjust the adhesive strength of the resin composition for forming the peelable layer. The tackifier resin (D) is compatible with the HP-LDPE (A) described above, and is contained in the sea portion of the sea-island structure in the peelable layer, which is thought to improve the strength. The tackifier resin (D) is selected from resins that have the function of imparting tackiness. Examples of the tackifier resin (D) include aromatic hydrocarbon resins, alicyclic hydrocarbon resins, aliphatic hydrocarbon resins, terpene resins, rosins, styrene resins, and coumarone-indene resins, with alicyclic hydrocarbon resins being preferred.

[0041] Examples of aromatic hydrocarbon resins include resins obtained by polymerizing fractions containing at least one vinyl aromatic hydrocarbon having 8 to 10 carbon atoms, such as vinyltoluene, indene, and α-methylstyrene, and resins obtained by copolymerizing these fractions with aliphatic hydrocarbon fractions. Examples of alicyclic hydrocarbon resins include resins obtained by cyclodimerizing and then polymerizing diene components in spent C4-C5 fractions, resins obtained by polymerizing cyclic monomers such as cyclopentadiene, and resins obtained by intranuclear hydrogenation of aromatic hydrocarbon resins (e.g., hydrogenated petroleum resins). Examples of aliphatic hydrocarbon resins include resins obtained by polymerizing fractions containing at least one mono- or diolefin having 4 to 5 carbon atoms, such as 1-butene, isobutene, butadiene, 1,3-pentadiene, and isoprene. Examples of terpene resins include α-pinene polymers, β-pinene polymers, dipentene polymers, terpene-phenol copolymers, α-pinene-phenol copolymers, and hydrogenated versions of these. Examples of rosins include rosins such as gum rosin, wood rosin, and tall oil, as well as modified products thereof, and examples of modified products include those that have been subjected to modifications such as hydrogenation, disproportionation, dimerization, esterification, etc. Examples of styrene-based resins include low-molecular-weight resinous polymers obtained by polymerizing styrene-based monomers such as styrene, vinyltoluene, α-methylstyrene, and isopropyltoluene.

[0042] The tackifier resin (D) is preferably a resin having a softening point of 85°C to 130°C, more preferably 100°C to 125°C, and even more preferably 110°C to 120°C. In general, a softening point of 85°C or higher tends to provide excellent heat resistance, while a softening point of 130°C or lower tends to provide excellent tackifying properties. The softening point of the tackifier resin (D) can be a value measured based on the softening point test method (ring and ball method) in accordance with JIS K 2207:2006.

[0043] When the peelable layer further contains a tackifier resin (D), the content of the tackifier resin (D) is preferably greater than 0% by mass and less than 25% by mass, relative to the total mass of the resin composition for forming the peelable layer. When the content of the tackifier resin (D) exceeds 0% by mass, relative to the total mass of the resin composition for forming the peelable layer, variation in adhesive strength to the adherend is suppressed. From the viewpoint of uniform adhesive strength, the content of the tackifier resin (D) is more preferably 3% by mass or more, even more preferably 5% by mass or more, and particularly preferably 7% by mass or more, relative to the total mass of the resin composition for forming the peelable layer. Furthermore, from the viewpoint of achieving a good balance between adhesion and releasability, the content of the tackifier resin (D) is preferably less than 25% by mass, more preferably 20% by mass or less, even more preferably 18% by mass or less, and particularly preferably less than 16% by mass, relative to the total mass of the resin composition for forming the peelable layer. That is, the content of the tackifier resin (D) is more preferably greater than 0% by mass and not more than 20% by mass, even more preferably 5% by mass or more and not more than 18% by mass, and particularly preferably 7% by mass or more and less than 16% by mass, relative to the total mass of the resin composition for forming the easily peelable layer.

[0044] The tackifier resin (D) in the easily peelable layer may be a commercially available product. Examples of commercially available tackifier resins (C) include hydrogenated alicyclic resins such as Alcon (registered trademark: the same applies hereinafter) P140 (manufactured by Arakawa Chemical Industries, Ltd., softening point 140 ° C.), Alcon P125 (manufactured by Arakawa Chemical Industries, Ltd., softening point 125 ° C.), Alcon P115 (manufactured by Arakawa Chemical Industries, Ltd., softening point 115 ° C.), Alcon P100 (manufactured by Arakawa Chemical Industries, Ltd., softening point 100 ° C.), and Alcon P90 (manufactured by Arakawa Chemical Industries, Ltd., softening point 90 ° C.).

[0045] When the easily peelable layer contains a tackifier resin (D), the total content of the HP-LDPE (A), PP (B), and tackifier resin (D) in the easily peelable layer preferably exceeds 90 mass% based on the total mass of the solid content in the easily peelable layer.

[0046] -Other Components- The easily peelable layer, more specifically the resin composition for forming the easily peelable layer, may contain an antistatic agent. Examples of antistatic agents that can be contained in the easily peelable layer include conductive polymers, nonionic surfactants, and anionic surfactants. Examples of antiblocking agents that can be contained in the easily peelable layer include silica and aluminosilicates (zeolites, etc.). Examples of slip agents that can be contained in the easily peelable layer include polyalkylene glycols such as polyethylene glycol and polypropylene glycol; hydrogenated castor oil, etc. When the easily peelable layer contains a slip agent, the content of the slip agent is preferably less than 1% by mass, and more preferably 0.5% by mass or less, relative to the total mass of the resin composition.

[0047] The content of the other components, excluding the thermoplastic elastomer and tackifier resin (D) contained in the resin, is preferably less than 2% by mass in total relative to the total mass of the easily peelable layer. In other words, the total content of HP-LDPE (A), PP (B), and optionally contained thermoplastic elastomer and tackifier resin (D) in the easily peelable layer is preferably more than 98% by mass and 100% by mass or less, more preferably 99% by mass or more and 100% by mass or less, and even more preferably 99.5% by mass or more and 100% by mass or less, relative to the total mass contained in the easily peelable layer.

[0048] The easily peelable layer can be obtained by preparing a resin composition for forming an easily peelable layer containing the above-mentioned components and molding it by a known method, for example, extrusion, etc. From the viewpoint of layer formability, the MFR of the resin composition for forming an easily peelable layer, measured in the same manner as described above, is preferably 10 g / 10 min to 50 g / 10 min, and more preferably 15 g / 10 min to 40 g / 10 min.

[0049] From the viewpoint of the balance between adhesion strength and ease of removability (peel strength), the thickness of the easily peelable layer is preferably 3 μm or more and less than 20 μm, more preferably 5 μm or more and less than 20 μm, and even more preferably 7 μm or more and less than 20 μm.

[0050] <Sealant layer> The paper container for liquids of the present disclosure has a sealant layer adjacent to the easily peelable layer. The sealant layer according to the present disclosure contains a polyethylene resin (C). The sealant layer is a layer that imparts heat-sealability to laminates when forming the paper container for liquids. In the paper container for liquids, the sealant layer is involved in forming the container, etc., and adheres the laminates that make up the paper container for liquid to each other by heat sealing, and serves as the outermost layer that comes into contact with the liquid contents.

[0051] -Polyethylene-based resin (C)- The sealant layer contains a polyethylene-based resin (C) (hereinafter also referred to as PE(C)). When the sealant layer contains PE(C), high adhesive strength of the paper container for liquids can be obtained. The polyethylene-based resin (C) (i.e., PE(C)) in the sealant layer preferably contains at least one selected from high-pressure low-density polyethylene and linear low-density polyethylene.

[0052] High-pressure low-density polyethylene, an example of a preferred embodiment of PE (C), is a low-density polyethylene resin obtained by a high-pressure method, similar to the HP-LDPE (A) contained in the easily peelable layer described above. Hereinafter, the high-pressure low-density polyethylene that can be contained in the sealant layer may also be abbreviated as HP-LDPE. The MFR of the HP-LDPE contained in the sealant layer, measured in accordance with JIS K 7210-1:2014 at 190°C and a load of 2160 g, is preferably 1.0 g / 10 min or more and 100 g / 10 min or less, more preferably 1.0 g / 10 min or more and 50 g / 10 min or less. The preferred melting point range of the HP-LDPE contained in the sealant layer is the same as that of HP-LDPE (A). The HP-LDPE contained in the sealant layer and the HP-LDPE (A) contained in the easily peelable layer described above may be the same or different.

[0053] Linear low-density polyethylene, another preferred embodiment of PE (C), is, as mentioned above, a copolymer obtained by copolymerizing ethylene with an α-olefin such as 1-butene using a metallocene catalyst, and is also referred to as L-LDPE. Compared to HP-LDPE, L-LDPE has a lower melting point and can form a harder film. The metallocene catalyst may be a metallocene-based catalyst (single-site catalyst), such as a combination of a metallocene catalyst component consisting of a zirconium compound having a ligand with a cyclopentadienyl skeleton and an organoaluminum oxy-compound catalyst component, or a multi-site catalyst, such as a combination of a highly active titanium catalyst component and an organoaluminum compound catalyst component. Taking into account mechanical strength and processability, the L-LDPE contained in the sealant layer should have a density of 900 to 940 kg / m. ３ is preferred, and 900 to 930 kg / m ３ Furthermore, the MFR of the L-LDPE measured in accordance with JIS K 7210-1:2014 under conditions of 190°C and a load of 2160 g is preferably 0.1 g / 10 min to 100 g / 10 min, more preferably 0.2 g / 10 min to 50 g / 10 min.

[0054] The content of PE(C) in the sealant layer is preferably more than 95% by mass, and more preferably 97% by mass or more, based on the total solid content in the sealant layer. A content of PE(C) in the sealant layer of more than 95% by mass means that the sealant layer is mainly composed of PE(C). The content of HP-LDPE(A) relative to the total mass of PE(C) in the sealant layer is preferably 50% by mass or more and 100% by mass or less, more preferably more than 60% by mass and 100% by mass or less, even more preferably 70% by mass or more and 100% by mass or less, particularly preferably 90% by mass or more and 100% by mass or less, even more preferably 95% by mass or more and 100% by mass or less, even more preferably 95% by mass or more and 100% by mass or less, still more preferably more than 95% by mass and 100% by mass or less, and particularly preferably 97% by mass or more and 100% by mass or less.

[0055] The content of L-LDPE relative to the total mass of PE (C) in the sealant layer is preferably 50% by mass or more and 100% by mass or less, more preferably more than 60% by mass and 100% by mass or less, even more preferably 70% by mass or more and 100% by mass or less, particularly preferably 90% by mass or more and 100% by mass or less, even more preferably 95% by mass or more and 100% by mass or less, and particularly preferably 97% by mass or more and 100% by mass or less.

[0056] —Other Components—The sealant layer may further contain other components to the extent that the effects are not impaired. Examples of other components include thermoplastic resins other than HP-LDPE and L-LDPE, thermosetting resins, plasticizers, antioxidants, UV absorbers, antistatic agents, surfactants, colorants, light stabilizers, foaming agents, lubricants, crystal nucleating agents, crystallization accelerators, crystallization retarders, catalyst deactivators, inorganic fillers, organic fillers, impact modifiers, slip agents, crosslinking agents, crosslinking aids, tackifiers, silane coupling agents, processing aids, mold release agents, hydrolysis inhibitors, heat stabilizers, antifogging agents, flame retardants, flame retardant aids, light diffusing agents, antibacterial agents, antifungal agents, dispersants, and antiblocking agents. When the sealant layer contains other components, the other components may be used alone or in combination of two or more.

[0057] Examples of thermoplastic resins other than PE(C) that the sealant layer may contain (also referred to as other thermoplastic resins) include polyolefins, ethylene-unsaturated carboxylic acid copolymers or ionomers thereof, ethylene-vinyl acetate copolymers (EVA), ethylene-α-olefin copolymer elastomers, etc. Examples of the α-olefins include propylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, etc. Commercially available products may be used as the other thermoplastic resins.

[0058] The thickness of the sealant layer is preferably 5 μm to 70 μm, more preferably 8 μm to 65 μm, and even more preferably 10 μm to 60 μm.

[0059] <Paper substrate layer> The paper container for liquid of the present disclosure includes a paper substrate layer. The paper substrate is not particularly limited as long as it can be used to form various liquid containers. Examples of paper substrates that constitute the paper substrate layer include fine paper, medium-quality paper, pure white roll paper, coated paper, single-sided art paper, double-sided art paper, mixed paper, synthetic paper, and paperboard. The paper substrate layer can be formed using known paperboard from the standpoint of strength, durability, etc. Because paper containers for liquid are also used for food, etc., it is preferable to use cup base paper made of virgin pulp as the paper substrate, but the raw material for the paper substrate layer is not limited to this. The paper substrate used for the paper substrate layer should preferably have a basis weight of 200 g / m ２ ~500g / m ２ , preferably 200 g / m ２ ~450g / m ２ and the density is 0.6 g / cm ３ ~1.1 g / cm ３ Examples of suitable paperboard include:

[0060] The paper substrate may have a surface coated with polyethylene that is heat-sealed via a sealant layer. The polyethylene coating the surface of the paper substrate that is heat-sealed is not particularly limited as long as it is an ethylene polymer that mainly contains structural units derived from ethylene. The surface to be heat-sealed is preferably an ethylene homopolymer containing components other than polyethylene, or an ethylene copolymer containing 50% by mass or more of structural units derived from ethylene relative to the entire polymer, and more preferably an ethylene homopolymer. It may also be coated with a resin containing components other than polyethylene. The thickness of the coating layer of the paper substrate that is heat-sealed via the sealant layer of the paper substrate is not particularly limited. The thickness of the coating layer can be, for example, 5 μm to 30 μm, and preferably 10 μm to 20 μm.

[0061] (Laminate Layer) The surface of the paper base layer may have a laminate layer containing a polyethylene resin on the surface for the purpose of improving adhesion to an adjacent easily peelable layer or a barrier layer, etc., which will be described later. The laminate layer can be formed by extruding and laminating PE resins, including HP-LDPE, L-LDPE, etc., using an extruder. Note that the laminate layer here refers to a layer that is provided separately from the polyethylene that coats the surface of the paper base material described above. When the paper container-forming laminate has a laminate layer, the thickness of the laminate layer is preferably 5 μm or more, and more preferably 8 μm or more, from the viewpoint of improving adhesiveness. There is no particular upper limit to the thickness of the laminate layer, but it can be, for example, 20 μm or less.

[0062] (Other Optional Layers) Any resin layer, colored layer, printed layer, etc. may be formed on the outer surface of the paper substrate, that is, the surface that does not come into contact with the contents.

[0063] <Layer structure of paper container for liquid> The paper container for liquid of the present disclosure is not particularly limited in its layer structure as long as it has the above-mentioned paper base layer, easily peelable layer, and sealant layer in this order, and may further have other layers, for example, a barrier layer in addition to the above-mentioned laminate layer.

[0064] (Barrier layer) The paper container for liquid of the present disclosure may further include a barrier layer between the paper base layer and the easily peelable layer. The barrier layer can be provided for the purposes of gas barrier properties, water vapor barrier properties, odor blocking properties, etc. By including a barrier layer, the protection of the liquid contents is improved, and for example, the diffusion of odors through the paper base layer of the contents can be more reliably prevented.

[0065] Examples of the barrier layer include metal foils such as aluminum foil, aluminum-deposited films such as aluminum-deposited polyester and aluminum-deposited polypropylene, silica-deposited films such as silica-deposited polyester, and transparent vapor-deposited films. Among these, the barrier layer preferably contains at least one material selected from aluminum foil, aluminum-deposited film, and transparent vapor-deposited film. The thickness of the barrier layer can be selected depending on the purpose, but from the viewpoints of mechanical strength and workability, it is preferably, for example, 3 μm to 20 μm, more preferably 4 μm to 15 μm, and even more preferably 5 μm to 15 μm.

[0066] In order to increase the adhesive strength between the barrier layer and an adjacent layer, the surface of the barrier layer on which another resin layer is laminated or the surface on which an optional adhesive layer is laminated may be subjected to a surface treatment. Examples of surface treatments include physical treatments such as corona treatment, plasma treatment, and flame treatment, and chemical treatments such as anchor coat treatment. Among these, it is preferable that the surface of the barrier layer on which the adhesive layer is laminated is subjected to corona treatment.

[0067] The configuration of a paper container for liquid will be described with reference to the drawings. Fig. 1 is a schematic diagram showing an example of a laminate (hereinafter also referred to as a paper container laminate) that forms a paper container for liquid of the present disclosure. The paper container laminate 10 shown in Fig. 1 has a paper base layer 12, an easily peelable layer 14, and a sealant layer 16 provided adjacent to the easily peelable layer 14. In the paper container laminate 10 shown in Fig. 1, the sealant layer 16 is the outermost surface on the inner side that comes into contact with the contents, and the paper base layer 12 side is the outermost surface of the paper container.

[0068] As optional layers, for example, a laminate layer for improving adhesion, a barrier layer for improving content protection, etc. may be further provided between the paper base layer 12 and the easily peelable layer 14 in FIG. 1, and a colored layer, a printed layer, etc. may be provided on the surface of the paper base layer 12 opposite to the sealant layer side.

[0069] - Other layers - In addition to the layers already described, other layers that may be optionally provided in the paper container for liquids of the present disclosure include an adhesive layer for improving adhesion between different layers, an inorganic layer, a hard coat layer, an anti-fouling layer, an anchor coat layer, etc.

[0070] (Adhesive Layer) The adhesive layer may be two adjacent layers, such as the barrier layer and easily peelable layer described above, or a layer for improving adhesion between the barrier layer and the paper base layer. When the paper container for liquids of the present disclosure has an adhesive layer, the adhesive layer may be a single layer or two or more layers. The adhesive layer may contain a known adhesive. The adhesive layer may contain, for example, an ionomer of an ethylene-unsaturated carboxylic acid copolymer. The thickness of the adhesive layer is preferably 5 μm to 50 μm, more preferably 10 μm to 30 μm, and even more preferably 10 μm to 20 μm.

[0071] The position of the other layer is not particularly limited as long as the effects of the present disclosure are achieved. The number of other layers may be one or two or more.

[0072] <Shape of Paper Container for Liquid> The paper container for liquid of the present disclosure may have any shape, and known paper container shapes can be applied. Examples of the shape of the paper container include a triangular paper container that is close to a regular tetrahedron, a so-called brick-shaped box-shaped paper container, and a gable-top box-shaped paper container, and the like. A brick-shaped box-shaped paper container or a gable-top box-shaped paper container is preferred.

[0073] FIG. 2 is a perspective view showing an example of a brick-shaped paper box container, which is a paper container for liquids according to the present disclosure. The brick-shaped paper box container 20 shown in FIG. 2 is a box-shaped container formed by folding a sheet of paper into a rectangular parallelepiped, with overlapping portions glued together to form the box-shaped container. In FIG. 2, the glued overlapping portions 22 are shown as dotted areas. The brick-shaped paper box container 20 has a protruding portion 24 on the top surface that is bent sideways to form a brick shape. One example is a configuration in which the protruding portion 24 is lifted upward on the top surface and the tip of the protruding portion is cut off to open the container. Another example is a configuration in which a spout made of resin or the like is formed on the top surface.

[0074] Figure 3A is a perspective view showing an example of a gable-top box-shaped paper container, which is a liquid paper container of the present disclosure. The gable-top box-shaped paper container 30 shown in Figure 3A is called a gable-top type because the top surface is folded in the shape of a gable roof. The glued overlapping portion 32 in the gable-top box-shaped paper container 30 shown in Figure 3A is shown as a dotted area. The gable-top box-shaped paper container 30 can be opened by unfolding the overlapping portion 32 at the top of the top surface.

[0075] 3B is a perspective view showing an example of a gable-top paper box container having a spout on the gable roof portion of the gable top. The gable-top paper box container 34 shown in FIG. 3B has a resin spout 36 on the side of the gable roof, and the liquid contents can be taken out by opening the spout. The spout 36 is preferably a fitting spout with an openable spiral groove, as it can be resealed.

[0076] <Preferable physical properties of paper container for liquid> The paper container for liquid of the present disclosure preferably has both high adhesion strength and easy releasability. Below, preferred physical properties for adhesion strength and peel strength, which is an index of easy releasability, of the paper container for liquid of the present disclosure are listed.

[0077] - Peel strength - When the overlapping portion of the laminate for forming a paper container for liquid of the present disclosure is heat-sealed at a gauge pressure of 0.2 MPa, a heating temperature of 180°C, and a sealing time of 3.0 seconds, the peel strength is preferably 20 N or more and less than 40 N, and more preferably 30 N or more and less than 40 N. If the peel strength is less than 20 N using the test method described below, the container may not be able to maintain its seal due to, for example, vibrations, temperature conditions, and stress during transport of the container, which may reduce the protection of the contents. Furthermore, if the peel strength exceeds 40 N, it may be difficult to open by hand.

[0078] The peel strength test method will now be described in more detail.

[0079] First, a low-density polyethylene (MFR (190°C, 2160 g load): 3.7 g / 10 min, density: 923 kg / m) was applied to one side of the paper substrate. ３) to a thickness of 20 μm to obtain a paper substrate layer. An easily peelable layer and a sealant layer are co-extruded on the surface of the paper substrate layer on which the low-density polyethylene is laminated, to obtain a laminate for forming paper containers. The obtained laminate is cut into samples 100 mm long and 300 mm wide, and the sealant layer sides of the samples are stacked so that the centers of the samples face each other. Next, heat sealing is performed under the following heat sealing conditions to obtain a test sample having a layer structure of paper substrate layer / polyethylene / easily peelable layer / sealant layer / sealant layer / easily peelable layer / polyethylene / paper substrate layer. The sample is then left to stand for 24 hours in an environment of 23°C and 50% RH.

[0080] When evaluating a laminate having a laminate layer between the polyethylene and the easily peelable layer, a test sample is obtained as follows: First, a low-density polyethylene (MFR (190°C, 2160 g load): 3.7 g / 10 min, density: 923 kg / m) is applied to one side of a paper substrate. ３ ) to a thickness of 20 μm to obtain a paper substrate layer. A laminate layer, an easily peelable layer, and a sealant layer are co-extruded on the surface of the paper substrate layer on which the low-density polyethylene is laminated to obtain a laminate for forming paper containers. HP-LDPE is used as the laminate layer. The obtained laminate is cut into samples 100 mm long and 300 mm wide, and the sealant layer sides of the samples are stacked so that the centers of the samples face each other. Next, heat sealing is performed under the following heat sealing conditions to obtain a test sample with a layer structure of paper substrate layer / polyethylene / laminate layer / easily peelable layer / sealant layer / sealant layer / easily peelable layer / laminate layer / polyethylene / paper substrate layer. The sample is then left to stand for 24 hours in an environment of 23°C and 50% RH.

[0081] (Heat sealing conditions) Sealing device: Heat seal tester (TP-701S manufactured by Tester Sangyo Co., Ltd.) Sealing temperature: 180°C Sealing time: 3.0 seconds Sealing pressure (gauge pressure): 0.2 MPa

[0082] Next, the test sample prepared above is cut into a size of 30 mm wide and peeled under the following peeling conditions to measure the maximum peel strength during peeling. Measurement is performed four times, and the average of the maximum peel strengths is taken as the peel strength (N / 30 mm). (Peel conditions) Peel test device: small tabletop tester (Shimadzu Corporation EZ-SX) Test speed: 300 mm / min Peel angle: 90 degrees Temperature: 23°C Humidity: 50% RH

[0083] -Bag Breakage Evaluation- The paper container for liquid of the present disclosure must be prevented from breaking due to peeling of the seal caused by impact during transportation and storage, and the liquid inside must be protected. From the perspective of protecting the liquid contents, it is desirable that the paper container for liquid of the present disclosure does not break in a bag breakage evaluation evaluated according to the following criteria. The test method is shown below.

[0084] A laminate for forming a paper container was obtained in the same manner as the above peel strength sample. The laminate was cut into samples 400 mm long and 300 mm wide, and the sealant layer sides of the samples were stacked together so that the centers of the samples faced each other. Next, three of the four sides were heat-sealed under the following heat-sealing conditions to obtain a bag-shaped test sample having a layer structure of paper base material / polyethylene / laminate layer / easily peelable layer / sealant layer / sealant layer / easily peelable layer / laminate layer / polyethylene / paper base material, or a layer structure of paper base material / polyethylene / easily peelable layer / sealant layer / sealant layer / easily peelable layer / polyethylene / paper base material, and this was left to stand for 24 hours in an environment of 23°C and 50% RH.

[0085] (Heat sealing conditions) Sealing device: Heat seal tester (TP-701S manufactured by Tester Sangyo Co., Ltd.) Sealing temperature: 180°C Sealing time: 3.0 seconds Sealing pressure (gauge pressure): 0.2 MPa

[0086] One liter of water is poured into the bag-shaped test sample prepared above, and the remaining side is heat-sealed under the heat-sealing conditions described above to obtain a bag-breakage test sample with internal dimensions of 360 mm length and 260 mm width. The bag-breakage test sample is then dropped perpendicularly from a height of 2 m above the ground, and it is observed whether or not the bag breaks after two drops.

[0087] - Pressure resistance evaluation - Because the contents of the paper container for liquids of the present disclosure are liquid, when pressure is applied from outside the container, stress is applied to the closure via the liquid contents, which may cause the bag to break due to pressure. It is desirable that the paper container for liquids of the present disclosure does not break when evaluated by the pressure resistance described below. (Test method) A laminate for forming a paper container is obtained in the same manner as the sample for peel strength described above. The laminate is cut into samples 150 mm long and 100 mm wide, and the sealant layer sides of the samples are stacked so that the centers of the samples face each other. Next, three of the four sides are heat-sealed under the following heat-sealing conditions to obtain a bag-shaped test sample having a layer structure of paper base material / polyethylene / laminate layer / easily peelable layer / sealant layer / sealant layer / easily peelable layer / laminate layer / polyethylene / paper base material, or a layer structure of paper base material / polyethylene / easily peelable layer / sealant layer / sealant layer / easily peelable layer / polyethylene / paper base material, and this sample is left to stand in an environment of 23°C and 50% RH for 24 hours.

[0088] (Heat sealing conditions) Sealing device: Heat seal tester (TP-701S manufactured by Tester Sangyo Co., Ltd.) Sealing temperature: 180°C Sealing time: 3.0 seconds Sealing pressure (gauge pressure): 0.2 MPa

[0089] 50 mL of water is poured into the bag-shaped test sample prepared above, and the remaining side is heat-sealed under the above heat-sealing conditions to obtain a pressure test sample with internal dimensions of 130 mm in length and 80 mm in width. A load of 150 kg is applied to the pressure test sample under the following pressure test conditions, and the test is carried out three times, and the presence or absence of rupture of the sample after the test is completed is observed. (Pressure test conditions) Pressure test device: Press Checker (PT-TAP, manufactured by Taisei Lamic Co., Ltd.) Load: 150 kg Pressurization time: 60 seconds

[0090] Sensory Evaluation: A laminate for forming a paper container was obtained in the same manner as the peel strength sample. The laminate was cut into samples 100 mm long and 300 mm wide, and the sealant layer sides of the samples were stacked together so that the centers of the samples faced each other. Next, heat sealing was performed under the following heat sealing conditions to obtain a test sample having a layer structure of paper base material / polyethylene / laminate layer / easily peelable layer / sealant layer / sealant layer / easily peelable layer / laminate layer / polyethylene / paper base material, or a layer structure of paper base material / polyethylene / easily peelable layer / sealant layer / sealant layer / easily peelable layer / polyethylene / paper base material. The sample was then left to stand for 24 hours in an environment of 23°C and 50% RH.

[0091] (Heat sealing conditions) Sealing device: Heat seal tester (TP-701S manufactured by Tester Sangyo Co., Ltd.) Sealing temperature: 180°C Sealing time: 3.0 seconds Sealing pressure (gauge pressure): 0.2 MPa Next, the test sample prepared above was cut into a size of 50 mm width, and the sample piece was grasped by hand and pulled outward to open, and the ease of opening was evaluated sensorily.

[0092] <Method for manufacturing paper container for liquid> The paper container for liquid of the present disclosure can be manufactured by preparing a paper container-forming laminate having the layer structure described above, folding it into a predetermined shape, and joining the overlapping portions. The paper container-forming laminate can be manufactured by forming an easily peelable layer and a sealant layer on a paper base material. When the paper container-forming laminate has a laminate layer, it can be manufactured by forming an easily peelable layer and a sealant layer on a paper base material having a laminate layer. Furthermore, to improve adhesion between the paper base material and an adjacent layer, a laminate layer may be provided between the paper base material and the easily peelable layer. The layers constituting the paper container-forming laminate can be formed by appropriately applying known laminate manufacturing methods, such as a method of applying a coating liquid to a paper base material in multiple layers, or a method of forming a film by co-extrusion of molten resins to form each layer constituting the laminate. Among these, from the viewpoint of ease of manufacturing, a method of forming each layer on a paper base material by co-extrusion is preferred.

[0093] The paper container for liquids of the present disclosure has excellent adhesion at the overlapping portions of the paper container-forming laminates, providing excellent protection for the liquid contents, stable sealing strength, and suppressing undesired peeling during storage or transportation, resulting in excellent protection of the contents. Furthermore, because the peel strength of the overlapping portions is within an appropriate range, the container can be easily opened and easily disassembled for recycling after use. Therefore, the paper container for liquids of the present disclosure has a wide range of applications and can be suitably used for a variety of liquids. In the paper container for liquids of the present disclosure, the joints at the overlapping portions are sealed by melt-bonding the resin layers together, making it suitable for use with, for example, edible oils, dairy products containing milk fat, and fruit juice drinks containing various ingredients.

[0094] The liquid paper container may be used to package liquids other than food and beverages, such as pharmaceuticals, industrial products, cosmetics, etc.

[0095] The liquid paper container of the present disclosure will be described in further detail below based on examples. However, the following examples are merely examples of the liquid paper container of the present disclosure, and it goes without saying that the present disclosure includes various modified examples.

[0096] In the examples and comparative examples shown below, the following materials were used: <Paper substrate layer> Cup base paper (manufactured by Oji F-Tex Co., Ltd., basis weight 250 g / m ２ ), low-density polyethylene (MFR (190 ° C, 2160 g load): 3.7 g / 10 min, density: 923 kg / m ３ ) 20 μm was laminated to form a paper substrate layer.

[0097] <High-pressure low-density polyethylene (A) (HP-LDPE (A))> HP-LDPE1 (MFR (190°C, 2160 g load): 23 g / 10 min, density: 918 kg / m ３ , melting point: 106°C) HP-LDPE2 (MFR (190°C, 2160g load): 70g / 10min, density: 916kg / m ３ , melting point: 104°C) HP-LDPE3 (MFR (190°C, 2160g load) 7.2g / 10min, density 918kg / m ３ , melting point: 108 ° C.)

[0098] <Propylene-based resin (B) (PP(B))> Homo PP1 (propylene homopolymer, MFR (230°C, 2160 g load): 3.0 g / 10 min, density: 910 kg / m ３ , melting point: 165°C) Homo PP2 (propylene homopolymer, MFR (230°C, 2160g load): 7.0g / 10min, density: 900kg / m ３ , melting point: 164 ° C.)

[0099] <Polyethylene Resin (C)> L-LDPE (linear low-density polyethylene, MFR (190°C, 2160 g load): 10 g / 10 min, density: 910 kg / m ３ , melting point: 112 ° C.)

[0100] <Tackifier Resin (D)> Tackifier Resin 1: Alicyclic hydrocarbon resin (manufactured by Arakawa Chemical Industries, Ltd., Alcon (registered trademark) P115)

[0101] <Additives> Release agent: erucic acid amide (ELA, manufactured by NOF Corporation) Slip agent: polyethylene glycol (PEG, manufactured by Nippon Fine Chemical Co., Ltd.)

[0102] [Examples 1 to 4 and Comparative Examples 1 and 2] <Preparation of Resin Composition 1 for Forming Peelable Layer> The materials were pre-mixed in a blending ratio of 17 parts by mass of HP-LDPE1, 33 parts by mass of HP-LDPE2, 34.8 parts by mass of Homo PP1 as PP (B), 15 parts by mass of tackifier resin (D), 0.1 part by mass of a roll release agent, and 0.1 part by mass of a slip agent, so that the charged amount was 10 kg. The mixture was then charged into a single-screw extruder having a screw diameter of 65 mmφ (effective screw length: L / D = 28) and melt-kneaded at a processing temperature of 240°C, to prepare Resin Composition 1 for Forming Peelable Layer (hereinafter also referred to as Composition 1). Of all the components in Composition 1, the total content of HP-LDPE (A), PP (B), and tackifier resin (D) was 99.8 mass%, and the content of HP-LDPE (A) was 59.0 mass% relative to the total content of HP-LDPE (A) and PP (B).

[0103] <Preparation of Resin Composition 2 for Forming Peelable Layer> The materials were pre-mixed in a blending ratio of 21 parts by mass of HP-LDPE1, 41 parts by mass of HP-LDPE2, and 38 parts by mass of Homo PP1 as PP(B) so that the charged amount was 10 kg, and the mixture was melt-kneaded under the same conditions as for Composition 1, to prepare Resin Composition 2 for forming a peelable layer (hereinafter also referred to as Composition 2). Of all the components in Composition 2, the content of HP-LDPE(A) was 62% by mass relative to the total content of HP-LDPE(A) and PP(B).

[0104] <Preparation of Resin Composition 3 for Forming Peelable Layer> The materials were pre-mixed in a blending ratio of 10 parts by mass of HP-LDPE1, 30 parts by mass of HP-LDPE2, and 60 parts by mass of Homo PP2 as PP(B) so that the charged amount was 10 kg, and the mixture was melt-kneaded under the same conditions as for Composition 1, to prepare Resin Composition 2 for forming peelable layer (hereinafter also referred to as Composition 2). Of all the components in Composition 3, the content of HP-LDPE(A) was 40% by mass relative to the total content of HP-LDPE(A) and PP(B).

[0105] The formulations of Compositions 1, 2, and 3 that constitute the easily peelable layer are shown in Table 1 below. In the table, "-" indicates that the component in question is not contained.

[0106]

[0107] The MFR of composition 1 measured under conditions of 190°C and a load of 2160 g was 32 g / 10 min, the MFR of composition 2 measured under the same conditions was 18 g / 10 min, and the MFR of composition 3 measured under the same conditions was 13 g / 10 min.

[0108] <Preparation of Laminate> In the embodiment with a laminate layer, a multilayer cast film forming machine was used to extrusion laminate a molten film consisting of the laminate layer / easily peelable layer / sealant layer so as to be bonded to the surface of the paper base layer on which the 20 μm low-density polyethylene was laminated, thereby producing a laminate for forming a paper container. In the embodiment without a laminate layer, a multilayer cast film forming machine was used to extrusion laminate a molten film consisting of the easily peelable layer / sealant layer so as to be bonded to the surface of the paper base layer on which the 20 μm low-density polyethylene was laminated, thereby producing a laminate for forming a paper container.

[0109] The laminate layer was formed using the HP-LDPE3 described above. The easily peelable layer was formed using the resin composition 1 for forming an easily peelable layer (composition 1) obtained above in Examples 1, 3, and 4, and the resin composition 2 for forming an easily peelable layer (composition 2) obtained above in Example 2. The easily peelable layer was formed using the L-LDPE described above in Comparative Example 1, and the resin composition 3 for forming an easily peelable layer (composition 3) obtained above in Comparative Example 2. The sealant layer was formed using the HP-LDPE3 or L-LDPE described above. The types of resins contained in the sealant layer are shown in Table 2 below.

[0110] The layer structure of the paper container-forming laminates of Examples 1 to 3 was cup base paper (paper base layer) / polyethylene (paper base layer) / laminate layer / easily peelable layer / sealant layer. The layer structure of the paper container-forming laminate of Example 4 was cup base paper (paper base layer) / polyethylene (paper base layer) / easily peelable layer / sealant layer. The multilayer cast film molding machine used above was a three-type, three-layer multilayer cast film molding machine manufactured by Tanabe Plastics Machinery Co., Ltd., and each molding machine was a single-screw extruder with a screw diameter of 40 mmφ and a die width of 500 mm. The coextrusion feed block was manufactured by EDI. The T-die setting temperature was 220°C. The thickness structure of each layer of the paper container-forming laminates of Examples 1 to 3 was laminate layer / easily peelable layer / sealant layer = 10 μm / 15 μm / 30 μm. The thickness configuration of each layer of the laminate for forming a paper container in Example 4 was such that the easily peelable layer / sealant layer was 15 μm / 30 μm.

[0111] Evaluation of the paper container for liquid of the present disclosure is obtained by folding the obtained paper container-forming laminate into a three-dimensional box shape and sealing the overlapping portions, i.e., the two sealant layers, by heat sealing. To evaluate the paper container for liquid, first, the physical properties of the obtained paper container-forming laminate were evaluated according to the following criteria.

[0112] <Evaluation of Peel Strength> The peel strength test method is as follows. ２ ) on one side of which was a low-density polyethylene (MFR (190°C, 2160 g load): 3.7 g / 10 min, density: 923 kg / m ３ ) to a thickness of 20 μm to obtain a paper substrate layer. A laminate layer, an easily peelable layer, and a sealant layer were co-extruded on the surface of the paper substrate layer on which the low-density polyethylene layer was formed, to obtain a laminate for forming a paper container. The obtained laminate for forming a paper container was cut into samples 100 mm long and 300 mm wide, and the sealant layer sides of the samples were stacked so that the centers of the samples faced each other. The samples were heat-sealed under the following heat-sealing conditions to obtain a test sample having a layer structure of paper substrate (cup base paper) / polyethylene / laminate layer / easily peelable layer / sealant layer / sealant layer / easily peelable layer / laminate layer / polyethylene / paper substrate (cup base paper), which was then left to stand for 24 hours in an environment of 23°C and 50% RH. The test sample corresponding to Example 4 had a layer structure of paper substrate (cup base paper) / polyethylene / easily peelable layer / sealant layer / sealant layer / easily peelable layer / polyethylene / paper substrate (cup base paper). In addition, in Example 4, taking into consideration the actual layer structure, the above layer structure was also used in the bag breakage evaluation, pressure resistance test, and sensory evaluation, which will be described later.

[0113] (Heat sealing conditions) Sealing device: Heat seal tester (TP-701S manufactured by Tester Sangyo Co., Ltd.) Sealing temperature: 180°C Sealing time: 3.0 seconds Sealing pressure (gauge pressure): 0.2 MPa

[0114] Next, the test sample prepared above was cut into a size of 30 mm wide and peeled under the following peeling conditions to measure the maximum peel strength during peeling. The measurement was performed four times, and the average of the maximum peel strengths during measurement was taken as the peel strength (N / 30 mm) of the laminate for forming a paper container. (Peel conditions) Peel test device: small tabletop tester (Shimadzu Corporation EZ-SX) Test speed: 300 mm / min Peel angle: 90 degrees Temperature: 23°C Humidity: 50% RH

[0115] The peel strength was evaluated according to the following evaluation criteria. Level A indicates practically acceptable performance. (Evaluation criteria) A: Peel strength is in the range of 20N or more and 40N or less B: Peel strength is less than 20N or more than 40N

[0116] <Bag Breakage Evaluation> A laminate for forming a paper container was obtained in the same manner as the above peel strength sample, and samples 400 mm long and 300 mm wide were cut out. The sealant layer sides of the samples were stacked together so that their centers faced each other. Next, three of the four sides were heat-sealed under the following heat-sealing conditions to obtain bag-shaped test samples having a layer structure of paper base material (cup base paper) / polyethylene / laminate layer / easily peelable layer / sealant layer / sealant layer / easily peelable layer / laminate layer / polyethylene / paper base material (cup base paper) or a layer structure of paper base material (cup base paper) / polyethylene / easily peelable layer / sealant layer / sealant layer / easily peelable layer / polyethylene / paper base material (cup base paper). The samples were then left to stand for 24 hours in an environment of 23°C and 50% RH.

[0117] (Heat sealing conditions) Sealing device: Heat seal tester (TP-701S manufactured by Tester Sangyo Co., Ltd.) Sealing temperature: 180°C Sealing time: 3.0 seconds Sealing pressure (gauge pressure): 0.2 MPa

[0118] One liter of water was poured into the bag-shaped test sample prepared above, and the remaining side was heat-sealed under the above heat-sealing conditions to obtain a bag-breakage test sample with internal dimensions of 360 mm in length and 260 mm in width. The bag-breakage test sample was then dropped perpendicularly from a height of 2 m from the ground, and it was observed whether or not the bag broke after two drops. The bag-breakage test was evaluated according to the following criteria. Level A represents performance that presents no practical problems. (Evaluation criteria) A: No bag breakage was observed B: Bag breakage was observed

[0119] <Pressure Test> A laminate for forming a paper container was obtained in the same manner as the above peel strength sample and cut into a size of 150 mm in length and 100 mm in width. The sealant layer sides of the cut samples were overlapped so that the centers of the samples faced each other. Next, three of the four sides were heat-sealed under the following heat-sealing conditions to obtain a bag-shaped test sample having a layer structure of paper base material (cup base paper) / polyethylene / laminate layer / easily peelable layer / sealant layer / sealant layer / easily peelable layer / laminate layer / polyethylene / paper base material (cup base paper) or a layer structure of paper base material (cup base paper) / polyethylene / easily peelable layer / sealant layer / sealant layer / easily peelable layer / polyethylene / paper base material (cup base paper). This sample was then left to stand in an environment of 23°C and 50% RH for 24 hours.

[0120] (Heat sealing conditions) Sealing device: Heat seal tester (TP-701S manufactured by Tester Sangyo Co., Ltd.) Sealing temperature: 180°C Sealing time: 3.0 seconds Sealing pressure (gauge pressure): 0.2 MPa

[0121] 50 mL of water was poured into the bag-shaped test sample prepared above, and the remaining side was heat-sealed under the above heat-sealing conditions to obtain a pressure test sample with internal dimensions of 130 mm in length and 80 mm in width. A load of 150 kg was applied to the pressure test sample under the following pressure test conditions, and the test was carried out three times, and the presence or absence of rupture of the sample after the test was completed was observed. (Pressure test conditions) Pressure test device: Press Checker (PT-TAP, manufactured by Taisei Lamic Co., Ltd.) Load: 150 kg Pressurization time: 60 seconds

[0122] The pressure resistance test was evaluated according to the following criteria. Level A is performance that presents no practical problems. (Evaluation criteria) A: No bag breakage observed B: Bag breakage observed

[0123] <Sensory Evaluation> The test method for the sensory evaluation is as follows. ２ ) on one side of which was a low-density polyethylene (MFR (190°C, 2160 g load): 3.7 g / 10 min, density: 923 kg / m ３ ) to a thickness of 20 μm to obtain a paper base layer. A laminate layer, an easily peelable layer, and a sealant layer were co-extruded on the surface of the paper base layer on which the low-density polyethylene layer was formed, to obtain a laminate for forming a paper container. The obtained laminate for forming a paper container was cut into samples 100 mm long and 300 mm wide, and the sealant layer sides of the samples were stacked so that the centers of the samples faced each other. The samples were heat-sealed under the following heat-sealing conditions to obtain test samples having a layer structure of paper base (cup base paper) / polyethylene / laminate layer / easily peelable layer / sealant layer / sealant layer / easily peelable layer / laminate layer / polyethylene / paper base (cup base paper) or a layer structure of paper base (cup base paper) / polyethylene / easily peelable layer / sealant layer / sealant layer / easily peelable layer / polyethylene / paper base (cup base paper), and these were left to stand for 24 hours in an environment of 23°C and 50% RH.

[0124] (Heat sealing conditions) Sealing device: Heat seal tester (TP-701S manufactured by Tester Sangyo Co., Ltd.) Sealing temperature: 180°C Sealing time: 3.0 seconds Sealing pressure (gauge pressure): 0.2 MPa

[0125] Next, the test sample prepared above was cut into a size of 50 mm in width, and the sample piece was grasped by hand and pulled outward to open, and the ease of opening was evaluated by sensory evaluation.

[0126] The sensory evaluation was performed according to the following evaluation criteria. Level A is a practically acceptable level of performance. (Evaluation criteria) A: Can be easily opened by both adult men and women B: Cannot be easily opened by both adult men and women

[0127] The results of each evaluation are shown in Table 2 below.

[0128]

[0129] As is clear from Table 2, the paper container laminates evaluated in Examples 1 to 4 maintained peel strength within an appropriate range, and bag-breaking tests and pressure tests confirmed that the peel strength was at a level that was practically acceptable. Furthermore, sensory evaluation also confirmed that the paper containers for liquids using the paper container laminates of Examples 1 to 4 achieved both good shelf life for the contents and easy peelability when opened. A comparison of Examples 1 and 3 reveals that using L-LDPE in the sealant layer provides sufficient airtightness while providing better peelability than using HP-LDPE. On the other hand, the paper container laminate of Comparative Example 1, which contained only L-LDPE for easy peelability, had good airtightness but a peel strength exceeding 40 N. Therefore, the sensory evaluation revealed that the paper containers for liquids using the paper container laminate of Comparative Example 1 were difficult to open by hand, even for adults, and were at a level that posed practical problems. Therefore, it can be seen that the paper container for liquids using the paper container laminate of Comparative Example 1 is difficult to disassemble for recycling after opening and use. Furthermore, the laminate for forming a paper container of Comparative Example 2, in which the easily peelable layer contained HP-LDPE and PP but the HP-LDPE content was less than 50 mass% relative to the total content of HP-LDPE and PP, had a peel strength of less than 20 N, which was at a level that was problematic for practical use.

[0130] [Example 5] The same cup base paper as used in Example 1 (manufactured by Oji F-Tex Co., Ltd., basis weight 250 g / m ２ ) was used as a paper substrate, and the paper substrate was coated with a low-density polyethylene (MFR (190°C, 2160 g load): 7.2 g / 10 min, density: 918 kg / m ３) 20 μm, and aluminum foil (Toyo Aluminum K.K., Aluminum Haku C-1N30, alloy number A1N30H-0) 7 μm were laminated in this order to obtain a paper substrate layer laminated with a barrier layer. A molten film consisting of a laminate layer, an easily peelable layer, and a sealant layer was extrusion laminated using a three-layer cast film molding machine so as to be bonded to the aluminum foil side of the paper substrate layer having the obtained barrier layer, thereby producing a laminate for forming a paper container. The layer configuration of the laminate for forming a paper container was paper substrate (cup base paper) / polyethylene (paper substrate layer) / aluminum foil (paper substrate layer) / laminate layer / easily peelable layer / sealant layer. The laminate layer was formed using the HP-LDPE3 described above. The peelable layer was formed using the above-described peelable layer-forming resin composition 1 (composition 1), and the sealant layer was formed using the above-described L-LDPE, with a thickness configuration of laminate layer / peelable layer / sealant layer=10 μm / 15 μm / 30 μm at a T-die set temperature of 220° C. The three-layer cast film molding machine used above was a three-layer cast film molding machine manufactured by Tanabe Plastics Machinery Co., Ltd., and both molding machines had a screw diameter of 40 mmφ, a T-die width of 500 mm, and a coextrusion feed block manufactured by EDI.

[0131] [Explanation of symbols] 10: Laminate for forming a paper container, 12: Paper base material layer, 14: Easily peelable layer, 16: Sealant layer, 20: Brick-shaped box-shaped paper container (paper container for liquids), 22: Overlapping portion (overlapping portion of laminate for forming a paper container), 24: Protruding portion of paper container, 30: Gable-top box-shaped paper container (paper container for liquids), 32: Overlapping portion (overlapping portion of laminate for forming a paper container), 34: Spout (spout made of resin)

[0132] The disclosure of Japanese Patent Application No. 2023-141789, filed on August 31, 2023, is incorporated herein by reference. All documents, patent applications, and technical standards mentioned in this disclosure are incorporated herein by reference to the same extent as if each individual document, patent application, and technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. A paper container for liquid comprising, in that order, a paper base layer, an easily peelable layer, and a sealant layer adjacent to the easily peelable layer, wherein the easily peelable layer contains a high-pressure low-density polyethylene (A) and a propylene-based resin (B), the content of the high-pressure low-density polyethylene (A) in the easily peelable layer is 50 mass% or more relative to the total content of the high-pressure low-density polyethylene (A) and the propylene-based resin (B), and the sealant layer contains a polyethylene-based resin (C).

2. The paper container for liquid according to claim 1, further comprising a barrier layer between the paper base layer and the easily peelable layer.

3. The paper container for liquid according to claim 2, wherein the barrier layer comprises at least one material selected from the group consisting of aluminum foil, aluminum vapor-deposited film, and transparent vapor-deposited film.

4. A paper container for liquids according to claim 1 or 2, wherein the polyethylene resin (C) in the sealant layer contains at least one selected from high-pressure low-density polyethylene and linear low-density polyethylene.

5. A paper container for liquids according to claim 1 or 2, wherein the melting point of the high-pressure low-density polyethylene (A) in the easily peelable layer is in the range of 100°C to 125°C.

6. The paper container for liquid according to claim 1 or 2, wherein the propylene-based resin (B) in the easily peelable layer contains a propylene homopolymer (B1).

7. A paper container for liquid as described in claim 1 or claim 2, wherein the total content of the high-pressure low-density polyethylene (A) and the propylene-based resin (B) in the easily peelable layer is 50 mass% or more and 100 mass% or less relative to the total mass of the solids contained in the easily peelable layer.

8. A paper container for liquid according to claim 1 or 2, wherein the thermoplastic elastomer content in the easily peelable layer is less than 10% by mass based on the total mass of solids contained in the easily peelable layer.

9. A paper container for liquids as described in claim 1 or 2, wherein the content of the polyethylene resin (C) in the sealant layer exceeds 95 mass% based on the total mass of solids contained in the sealant layer.

10. A paper container for liquid according to claim 1 or 2, wherein the easily peelable layer further contains a tackifier resin (D).

11. A liquid paper container as described in claim 10, wherein the total content of the high-pressure low-density polyethylene (A), the propylene-based resin (B), and the tackifier resin (D) in the easily peelable layer exceeds 90 mass% based on the total mass of solids contained in the easily peelable layer.

12. The liquid paper container according to claim 1 or 2, which is a brick-type box paper container or a gable-top type box paper container.

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